1. Field of the Invention
The present invention relates to a method of producing epoxide by performing epoxidation of an olefin compound. In particular, the present application relates to a method for preparing an epoxide by using a molecular sieve as a catalyst.
2. Description of Related Art
Methods of producing an epoxide include an epichlorohydrin method, a co-oxidation method, a direct oxidation method and the like. The epichlorohydrin method produces chlorine waste, which causes damage to the environment. The co-oxidation method involves complex procedures, with various co-products. The direct oxidation method can be divided into a direct oxidation by oxygen and a direct oxidation by peroxide. The direct oxidation method by oxygen produces an epoxide by using pure oxygen as a reactant, is simple and produces no intermediate. However, the direct oxidation method by oxygen has lower selectivity of products. Therefore, the direct oxidation method by peroxide is widely used. In the direct oxidation method by peroxide, a titanium-silicon molecular sieve is generally used as a catalyst, and the catalyst is easily separated from products. The direct oxidation method by peroxide would not cause damages to the environment, and not consume large amounts of oxygen. However, the epoxide selectivity and production rate of the direct oxidation method by peroxide still need to be improved.
U.S. Pat. No. 4,824,976, U.S. Pat. No. 4,937,216, U.S. Pat. No. 5,646,314 and U.S. Pat. No. 5,675,026 disclose the production of an epoxide by performing the direct epoxidation of olefin compounds using a titanium-silicon molecular sieve as a catalyst. In order to increase the selectivity and yield of epoxide, a coagent such as aqueous alkaline, non-alkaline (neutral and acidic) carboxylate, alcohols, halides, nitrates or phosphates of alkali metals or alkaline-earth metals can be added before the reaction, during the reaction, or before and during the reaction.
Although the addition of the aforementioned coagent during the method of producing an epoxide can increase the selectivity rate and yield of epoxide, the practical use of the additive results in many defects. For example, alkali metal ions and alkaline earth metal ions reduce the conversion rate of hydrogen peroxide; another example of defect is that the reactivity and the solubility of the additive influence the selectivity of epoxide. Further, the reaction system needs extra water content, which leads to an increase in the formation of by-products. Moreover, the isolation of the additive needs increased energy consumption, the additive that contains H+ ions results in corrosion of equipment; and the presence of additives containing fluorine ions would destroy the structure of catalyst.
Therefore, there is a need to provide a substance for improving selectivity and yield of epoxide without the aforementioned defects.